Peter Hamm , Nov 29, 2010; 08:17 a.m.
First... if you don't need the ability to drive old-style AF lenses (screwdrive), and can live with the limitations of the very small D3100 (too small for my hands, but ymmv), the lack of a top display (I use this a lot, but would I miss it? not so sure) and without CLS flash control (I use this sometimes and love it, but could probably live without it truth be told), then maybe skip the D90.
Also, the D3100 lacks DoF preview. I myself thought I would really love having it but almost never use it. Again, the big thing that would kill that camera for me (or something like the D5000 or the eventual D5100 or whatever) is the small size. It's just too small.
If you can stand lens changes, there are better options than the 18-200 (which I had and LOVED). For instance, a combo of a used 18-70 and refurb or used 70-300 VR would be about the same price as a new (or maybe even a used) 18-200. That combo will be, in my experience, about the same from 18-70 but much better from 70 on up.
If you are a snapshop/vacation photographer who never prints above 8 x 10 or never views photos except on the computer (a "growing" class of photographer... I myself print about 2% of my photos... even my good ones... above 5 x 7), and you must have a "one-lens solution"...
then skip the 18-200 and get a 16-85, cropping at the long end when necessary. The 16-18 range is more useful than the 85-200 range imho.